In many systems utilizing a microprocessor and/or field-programmable gate array (FPGA), multiple supply voltages are needed. For example, a microprocessor-based system may require separate supply voltages for the input/output (I/O) logic circuits (also referred to as the “logic outer ring”) and the processor core. Typically, the I/O circuitry requires a 3.3 volt DC supply, while the microprocessor requires a 1.5 volt DC supply. If the system also (or alternatively) includes an FPGA, the FPGA core may require a 2.5 volt DC supply.
Furthermore, such processor-based systems may have particular power sequencing requirements to be followed during power-up and power-down operations. For example, in microprocessor-based systems, most control logic originates in the processor core. According, if the I/O circuitries were powered up before the processor core, the I/O pins of both the processor and peripheral devices may simultaneously be configured as outputs, thereby contending with one another for the control of the bus. This may cause excessive current to flow between the processor and peripheral devices.
Also, a microprocessor core is separated from the I/O circuitry by certain isolation structures. Powering up the I/O before the core may cause current to flow between these structures, thereby reducing the operating life of the reliability of the system. Thus, it is important that the microprocessor core supply is powered up before the I/O supply.
In microprocessor and FPGA systems, it is also important to bring the core and I/O voltages supplies to their normal operating levels in a timely manner. This limits the in-rush currents occurring at power-up, thereby reducing stress on various components in the system (e.g., transition and filter capacitors).
In order to control the power supplies to the core and logic outer ring, various conventional systems utilize dual output control devices based on linear regulators. However, linear regulators are inefficient because they experience high thermal losses and have no tracking abilities. Other types of conventional power control devices consist of dual output DC/DC converters. However, conventional converters, do not perform sequencing on their outputs, and therefore require additional circuitry to implement power sequencing.